1. Field of the Invention
The present invention relates to a stage apparatus capable of detecting the position of a movable member with precision and also relates to an image projector apparatus and an imaging apparatus each having this stage apparatus.
2. Description of the Related Art
A shake reduction (image shake correction/image stabilizing/anti-shake) system designed as an in-body shake reduction system which drives an image sensor in a camera body of an SLR camera system to perform an image shake correction operation is known in the art, wherein the image sensor is driven in the X-direction (the X-axis direction) and the Y-direction (the Y-axis direction), which are orthogonal to an optical axis, using oblong-shaped planar drive coils and permanent magnets, and the image sensor is also driven in the Z-direction (the Z-axis direction), which coincides with the optical axis direction, by a piezoelectric actuator. This type of shake reduction system is disclosed in Patent Literature 1.
It is known in the art for this type of related-art shake reduction system to be equipped with a position detector in which a Hall sensor is provided in the air-core area of each drive coil in order to detect the positions of the image sensor in the X-direction and the Y-direction in a plane (optical-axis-orthogonal plane) orthogonal to the optical axis of the image sensor and the rotational angle of the image sensor in this orthogonal plane.
[Patent Literature 1] Japanese Unexamined Patent Publication No. 2012-226205
However, when the image sensor is driven in the Z-direction (along the optical axis), a variation in position of the image sensor in the Z-direction causes the distance between each Hall sensor and the associated permanent magnet(s) to vary, thus causing the magnetic flux density to vary. This variation causes the output of each Hall sensor to vary, which makes it difficult to detect the positions of the image sensor in the X-direction and the Y-direction with precision. In addition, variations in position of the image sensor in the X-direction and the Y-direction make it difficult to detect the position of the image sensor in the Z-direction with high precision.